Cobalt Ferrite And The Stress And The Performance Research Of The Magnetoelectric Composite Films

With the development of thin film deposition techniques, it becomes possible toproduce thin films with good quality and advanced mircodevices with complexstructures. The coexistence of ferroelectric, ferromagnetic and magnetoelectricproperties in multiferroic magnetoelectric （ME） materials brings about novel structuraland schematic designs for new devices. The existence of a cross-coupling between themagnetic and electric orders enables the control of the ferroelectric polarization by amagnetic field and, conversely, the manipulation of magnetization by an electric field.Therefore, multiferroic magnetoelectric materials have great values for potentialapplications. Recently, multiferroic magnetoelectric thin films have been studiedextensively, and could be uesed for new memories and magnetic sensors in future.Residual stress is very common in thin films deposited by sol-gel method. The filmcracking presents when the stress is very large, and tends to strongly influence theproperties of thin films. The stress state in single-phase CoFe₂O₄（CFO） and compositeCoFe₂O₄/Pb(Zr_0.52Ti_0.48)O₃（PZT） thin films were studied by using Raman spectroscopyand finite element analysis （FEA）. The compressive stress of single-phase CFO thinfilms is about1.76GPa when the annealing temperature is700°C. And the stress ofCFO layer of CFO/PZT laminate composites is also compressive, about1.9GPa,however, the thermal stress of PZT layer is much smaller, about0.25GPa.Because the magnetostrictive coefficient of CFO and the piezoelectric coefficientof PZT are both very large, therefore, the magnetoelectric effect of CFO/PZTmultiferroic laminate composites is great. First, we have studied the magnetic propertiesof Co-ferrite thin films with different pyrolysis temperature, annealing temperature andfilm thickness. Then, CFO/PZT multiferroic composites were studied with differentannealing temperature and the film deposited order. The Raman scattering studies oncomposite thin films demonstrate that the deposition order of CFO and PZT leads todifferent stress state in the composite thin films, and causes significant influence on theferroelectric and ferromagnetic properties. It has beed observed good ferromagneticproperties, but due to some reasons, the ferroelectric properties in composite thin films are poor.